The present invention is drawn toward the controlling of orifice plate puddling of ink-jet inks having spreading vehicles. More specifically, the present invention is drawn toward compositions and methods of selecting dyes for use with spreading vehicles, such as 1,2-hexanediol vehicles, without added surfactant.
Thermal ink-jet printers provide an effective means of propelling ink-jet inks onto various media including paper. These printers can accomplish this by using resistive heater elements for heating the ink to a boil, and propelling the ink through an overlying orifice plate. Specifically, a typical ink-jet printhead has an array of precisely formed nozzles located on a nozzle plate and attached to an ink-jet printhead substrate. The substrate incorporates an array of firing chambers that receive liquid ink (colorants dissolved or dispersed in a solvent) through fluid communication with one or more ink reservoirs. Each chamber has a thin-film resistor located opposite the nozzle so ink can collect between the firing resistor and the nozzle. Upon energizing a particular resistor element, a droplet of ink is expelled through the nozzle toward a print medium. Such printers, as typified by the Hewlett-Packard DeskJet(trademark) and DesignJet(trademark) printers, are desirable for use for several reasons. For example, thermal ink-jet printers have a relatively fast throughput while being relatively inexpensive to run. Additionally, these printers are relatively easy to use, and the ink is easily replaced.
There are several other reasons that ink-jet printing has become a popular way of recording images on various media surfaces, particularly paper. Some of these reasons include low printer noise, capability of high-speed recording, and multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers. However, though there has been great improvement in ink-jet printing, accompanying this improvement are increased demands by consumers in this area, e.g., higher speeds, higher resolution, full color image formation, increased stability, new applications, etc. As new ink-jet inks are developed, there are several traditional characteristics to consider when evaluating the ink in conjunction with a printing surface or substrate. Such characteristics include edge acuity and optical density of the image on the surface, dry time of the ink on the substrate, adhesion to the substrate, lack of deviation of ink droplets, presence of all dots, resistance of the ink after drying to water and other solvents, long-term storage stability, good dot size and dot gain, color-to-color bleed alleviation, acceptable coalescence, and long term reliability without corrosion or nozzle clogging. Though the above list of characteristics provides a worthy goal to achieve, there are difficulties associated with satisfying all of the above characteristics. Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met. Thus, most commercial inks for use in ink-jet printers represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed requirements.
In general, ink-jet inks are either dye- or pigment-based inks. Dye-based ink-jet inks generally use a soluble colorant that is usually water-based to turn the media a specific color. Alternatively, pigmented inks typically use a dispersed colorant to achieve color. In many cases, the line quality and accuracy of plots produced by pigment-based inks can be superior to that of dye-based inks. However, certain challenges exist with pigments because the colorant is present as dispersion. With pigmented inks, solid particles are jetted with a vehicle and the solid particles adhere to the surface of the substrate. Once the water in the solution has evaporated, the particles will generally not redisperse, thereby producing a dried image.
As dye-based ink-jet inks have become more accurate as to their printability, increased interest in providing such inks has occurred. However, the problems associated with puddling of these ink-jet inks, particularly on the orifice plate of the ink-jet pen, have been problematic.
The present invention is drawn to compositions and methods related to ink-jet inks that exhibit reduced puddling at the orifice plate of an ink-jet ink pen. First, a method of selecting a dye for use with a spreading vehicle can comprise the steps of evaluating a first dye having polar atoms and a second dye having polar atoms to determine a first polarity index and a second polarity index, respectively; and selecting the first dye or the second dye for inclusion in the spreading vehicle based upon a comparison of the first polarity index and the second polarity index.
Alternatively, a method of evaluating a dye and formulating an ink-jet ink can comprise the steps of providing a spreading ink-jet ink vehicle; selecting a dye or mixture of dyes to be evalulated for inclusion in the spreading ink-jet ink vehicle; determining the ratio of polar atoms to carbon atoms within the dye; selecting a desired polarity index ratio range; and admixing the dye with the spreading ink-jet ink vehicle if the ratio is within the desired polarity index ratio range.
Additionally, an ink-jet ink composition exhibiting reduced orifice plate puddling can comprise an ink-jet ink vehicle containing 7% to 15% by weight of a 1,2-hexanediol solvent in the absence of added surfactant; and an effective amount of a dye having a normalized polarity index from about 7 to 12, wherein the normalized polarity index is calculated according to the following formula:             (              number        ⁢                  xe2x80x83                ⁢        of        ⁢                  xe2x80x83                ⁢        polar        ⁢                  xe2x80x83                ⁢        atoms            )        xc3x97    10        (          number      ⁢              xe2x80x83            ⁢      of      ⁢              xe2x80x83            ⁢      carbon      ⁢              xe2x80x83            ⁢      atoms        )  
and wherein the number of polar atoms is the number of oxygen, nitrogen, sulfur, phosphorus, and halogen atoms (particularly chlorine, bromine, and iodine) within the dye.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the exemplary embodiments, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
The singular forms xe2x80x9ca,xe2x80x9d xe2x80x9can,xe2x80x9d and, xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to xe2x80x9ca dyexe2x80x9d includes reference to one or more of such dyes.
As used herein, xe2x80x9ceffective amountxe2x80x9d refers to the minimal amount of a substance or agent, which is sufficient to achieve a desired result. For example, an effective amount of an xe2x80x9cink vehiclexe2x80x9d is the minimum amount required in order to create an ink composition, while maintaining properties necessary for effective ink jetting.
As used herein, xe2x80x9cink vehiclexe2x80x9d or xe2x80x9cspreading ink-vehiclexe2x80x9d refers to the composition in which the polar dyes are added to provide ink-jet ink compositions. Ink vehicles are well known in the art, and a wide variety of ink vehicles may be used with the methods and ink composition of the present invention. Preferably, 1,2-hexanediol solvent based ink-vehicles provide good spreading and jetting characteristics. Further, the ink-vehicle can be defined by many other known components, but preferably excludes the presence of traditional surfactants.
An xe2x80x9cink-jet inkxe2x80x9d or xe2x80x9cink compositionxe2x80x9d comprises a spreading ink vehicle, a dye, and water.
One important factor in obtaining good photographic image quality on photographic media is to provide ink-jet inks comprising a vehicle that spreads well. Such vehicles can form dots that are less visible (for less grain) and hide printer artifacts like banding. However, these types of highly spreading vehicles also have a propensity to puddle on the orifice plate of the ink-jet print head. This puddling causes misdirected drops in the form of satellite spotting leading to poor image quality.
It has been discovered that polar dyes such as RB31 and DB199, when added to spreading vehicles, such as 1,2-hexanediol vehicles in the absence of added surfactant, reduces or substantially eliminates the extent of puddling on the orifice plate. In the prior art, prior solutions used to prevent this puddling included the use of certain types and levels of surfactants. However, often surfactants lead to poor dot spreading, particularly on photographic type media. With the present invention, highly polar dyes can be used with spreading vehicles, such as 1,2-hexanediol based vehicles in particular, solving many problems of the prior art. First, as mentioned, reduced puddling on the orifice plate can be realized. Because of this reduced puddling, better drop directionality and less banding visible on the printed image is present. Additionally, these inks help maintain good nozzle health due to the maintaining of a cleaner orifice plate. Good nozzle health is one factor that contributes to nozzle reliability.
With this in mind, a method of selecting a dye for use with a spreading vehicle can comprise the steps of evaluating a first dye having polar atoms and a second dye having polar atoms to determine a first polarity index and a second polarity index, respectively; and selecting the first dye or the second dye for inclusion in the spreading vehicle based upon a comparison of the first polarity index and the second polarity index.
Alternatively, a method of evaluating a dye and formulating an ink-jet ink can comprise the steps of providing a spreading ink-jet ink vehicle; selecting a dye to be evaluated for inclusion in the spreading ink-jet ink vehicle; determining the ratio of polar atoms to carbon atoms within the dye; selecting a desired polarity index ratio range for the ratio; and admixing the dye with the spreading ink-jet ink vehicle if the ratio is within the desired polarity index ratio range.
With either of the above methods, preferably, the spreading vehicle contains from 7% to 15% of a 1,2-hexanediol solvent. Additionally, the use of spreading vehicles having no added surfactant is also desired.
With the present methods, the polarity index or ratio of polar atoms to carbon atoms of the dye can be ascertained according to a simple formula, provided below. With many dyes, this calculation can provide a value between 0.3 and 1.2, for example. This value can be normalized by multiplying the ratio value by 10. In one preferred embodiment, a desired polarity index can be from about 0.7 to 1.2. Still more preferred is a desired polarity index from about 0.8 to 1.0. If normalized, the preferred values will be from 7 to 12, and the more preferred values will be from 8 to 10. Both of these figures describe the same dye properties. Normalization is merely applied to the ratio values for convenience.
To illustrate a process of assigning or ascertaining a polarity index, Formula 1 is provided below:                                           (                          number              ⁢                              xe2x80x83                            ⁢              of              ⁢                              xe2x80x83                            ⁢              polar              ⁢                              xe2x80x83                            ⁢              atoms                        )                    xc3x97          10                          (                      number            ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            carbon            ⁢                          xe2x80x83                        ⁢            atoms                    )                                    Formula 1            
In Formula 1 above, the numbers of polar atoms that can be counted include oxygen, nitrogen, sulfur, phosphorus, and halogen atoms, e.g., chlorine, bromine, and iodine. Hydrogen is ignored in this calculation. Next, the number of carbon atoms is counted and a positive value is assigned. As mentioned, the multiplication factor of 10 is included to normalize the index to an integer value. Typically, the higher the number, the more polar the dye is, and thus, the more water soluble.
To illustrate this formula by way of example, the dye Acid Red 52 can be considered. Acid Red 52 has a chemical structure that is as follows: C27H28N2O7S2. According to Formula 1, the following calculation can be carried out:             (              2        +        7        +        2            )        xc3x97    10    27
Thus, according to this simple calculation, the polarity index for Acid Red 52 is 4.1. It turns out that Acid Red 52 is a dye that, when present in a spreading vehicle, produces a significant amount of puddling on the orifice plate of an ink-jet pen. This is particularly true with ink-jet inks having spreading vehicles containing 1,2-hexanediol and in the absence of added surfactant.
After considering several dyes present in a 1,2-hexanediol spreading vehicle, it was discovered that dyes having a polarity index greater than about 7 produced ink-jet inks exhibiting no, or at least reduced, puddling on the orifice plate. More specifically, polarity index values from about 8 to 9 produced the best results. Representative dyes that have a polarity index greater than about 7 include the following: RB31, RR23, RR180, DB199, and M377.